Lindt did not disclose the price of the deal that makes it the third biggest chocolate producer in the United States behind Hershey and Mars and enables it to diversify further beyond the European market where it gets the largest chunk of its sales.

"This biggest and most important strategic acquisition to date in Lindt & Spruengli's history is a unique opportunity for us to expand our North American chocolate business," Lindt chairman Ernst Tanner said.

In March, it said its North American sales should top $1bn this year. With the addition of Russell Stover, sales in the region should exceed $1.5bn in 2015, the company said.